The present invention relates generally to diagnostic immunoassays and material useful therein More particularly, the present invention relates to employing colloidal non-metal particles, especially selenium in specific binding assays to determine the presence of small quantities of an analyte of interest
Various analytical procedures are commonly employed in assays to determine the presence and/or concentration of substances of interest or clinical significance in fluids or other materials. Such clinical significant or interesting substances are commonly termed "analytes" and can include, for example, antibodies, antigens, and the broad category of substances commonly known by the term "ligands". Particularly, with respect to the diagnosis and treatment of disease or other conditions of the human body, the accurate determination, on a timely basis, of the presence or amount of certain analytes can have a profound influence on the ability of health care professionals to treat and manage pathological physical disorders or make an early and accurate determination of physiological conditions such as pregnancy.
Many diagnostic immunoassays are known which generally employ the specific binding characteristics that exist between an analyte or protein and a specific antibody tagged with some traceable substituent. Assays of these type include, for example, radioimmunoassay (RIA), free radical assay technique (FRAT), enzyme immunoassay technique (EIA), and immunofluorescence techniques such as fluorometric analysis and fluorescence polarization. Analytes of interest have also been detected and/or quantified using metal sol particle immunoassay techniques, as described in U.S. Pat. No. 4,313,734 to Leurverinq. In Leurverinq, colloidal metal particles of at least 5 nm are coupled to binding protein and employed as an aqueous sol dispersion in immunochemical techniques such as "sandwich" assays and homogeneous agglutination assays.
While the above techniques can be effective, they are subject to improvement. For example, although sensitive, a radioimmunoassay requires handling of radioactive compounds and use of sensitive instrumentation, such as a scintillation counter. Enzyme immunoassays are widely used; however, in general EIA's are not sensitive enough to detect small amounts of immunogens. Immunoassays employing metal sols are subject to limited detection range (i.e, wavelenqth range to monitor reaction) thereby requiring careful calibration of the instrument employed to monitor the change in optical properties of a sample.
Accordingly, there is a need for an improved method for conducting an immunoassay exhibitinq both high sensitivity and a wide detection range for analytes and proteins of interest.